In a single cell environment, an asynchronous channel can be used if time synchronization is not decided. In a multi-cell environment, especially, if a mobile station transmits a signal a neighboring cell, time synchronization may not be decided. When a mobile station transfers a structural control signal of an action mode of a neighboring cell or interference related information under a multi-cell environment or transfers a control signal or data to a neighboring cell without through a serving cell under a coordinated multi-point (CoMP) environment, an asynchronous channel is used preferably. The mobile station may transmit a control signal or data if time synchronization is not decided. In this case, the mobile station may perform communication with a relay station and a femto station.
A main example of the asynchronous channel includes an uplink synchronization channel referred to as a random access channel or a ranging channel. The uplink synchronization channel is to measure transmission timing of uplink waves when the mobile station accesses a base station. The uplink synchronization channel is used during a basic procedure for receiving uplink resources after a mobile station accesses a base station. Accordingly, the uplink synchronization channel is used when the mobile station initially turns on the power within a serving channel or accesses the serving cell in a sleep mode or an idle mode, or when the mobile station performs handover to a neighboring cell.
The related art does not suggest an asynchronous channel in addition to an uplink synchronization channel. This is because that the related art is based on an operation of a single cell. However, in accordance with the advent of relay and CoMP, the mobile station has performed multi-cell operation with neighboring cells. Also, the mobile station may restrict a multi input multi output (MIMO) structure, which can be used in a neighboring cell, to reduce inter-cell interference, or may recommend the MIMO structure to improve receiving strength of a signal.
In case of the single cell operation, the serving cell may continue to perform timing tracking of the mobile station so as to adjust a timing error to a cyclic prefix (CP) length.
However, under the multi-cell environment, the mobile station may perform communication with a cell other than its serving cell. The mobile station may receive signals from multiple cells or feed the signals back to the multiple cells, or may transmit a signal to a neighboring cell to manage inter-cell interference. Also, a relay node may feed a signal back to a macro base station, or CoMP transmission and reception or handover may be performed. Moreover, the mobile station or unit base stations may transmit a control signal or data to another mobile station or base station.
However, even though cells share timing information by designating a series of timing advances under the multi-cell environment, the cells cannot maintain such timing information. For this reason, the timing advances should be measured continuously for correction by neighboring cells for continuous operation, or a synchronization process in view of a network should be performed separately so that the mobile station accesses the multiple cells without any problem.